This application is a national stage of International Application No. PCT/EP2006/008904, filed Sep. 13, 2006, the entire disclosure of which is herein expressly incorporated by reference.
The present invention relates to apparatus for humidifying a gas flow, including means for separating excess water from the gas flow. The invention is particularly but not exclusively applicable for humidifying fuel gas and oxidant gas used in a fuel cell for automotive applications.
A known type of fuel cell has a polymer electrolyte membrane in which hydrogen forming a fuel gas is passed over one side of the membrane (the anode). In response to an applied electrical load an electrochemical reaction takes place in which hydrogen ions migrate through the membrane to combine with oxidant (usually derived from air) on the other side (or cathode) of the membrane. It is necessary for both the hydrogen gas and the air, which are kept in separate streams, to be humidified to ensure that a necessary quantity of water passes through both sides of the fuel cell where it serves to enhance the electrochemical action and also to prevent the drying out of the membrane, which would lead to poor efficiency in the electrochemical reaction and damage the fuel cell, or at least reduce its service life.
German patent document DE 100 28 133.8 discloses apparatus which is particularly suitable for humidifying a process gas flow in a fuel cell system. The humidified device comprises three sections, a spray chamber, a heat exchanger region, and a water separator. Water is atomized and injected into the spray chamber, where it is mixed with the flow of the gas. In the heat exchange region, heat exchange means are provided which utilize the heat in the gas to at least partially evaporate water to humidify the gas and to enable the excess water to be at least partially condensed. To ensure that satisfactory humidification takes place, a greater amount of water is atomized than is theoretically required to achieve a relative humidity of the gas of 100 percent. The excess water is collected in a water collector or separator located below the heat exchanger region.
The humidified device and water separator described have disadvantages when used in an automotive application, in particular, in coping with the g-forces which occur during cornering and changes in angular position of the vehicle when the vehicle is on a sloping surface. This can lead to inefficient drainage and reduced water separation. Thus, excess water can lie on the bottom of the separator where it can be re-entrained by the gas flow and, in extreme conditions, an excess of water can enter the fuel cell, reducing its efficiency.
One object of the present invention is to provide a humidifying apparatus incorporating a water separator, which is much less sensitive to g-forces than the known device.
This and other objects and advantages are achieved by the humidification apparatus according to the present invention in which an atomized liquid is combined with a gas flow in a spray chamber to humidify the gas. The combined atomized liquid and gas are passed through a gas flow passage which comprises a generally U-shaped passage having a first generally vertical part through which the atomized liquid and gas stream pass to a lower part. From there, the gas stream passes generally vertically upwardly to an outlet. According to a feature of the invention, the lower part of the passage incorporates an opening through which excess water separated out from the gas stream can pass to a water separator. The opening is closable by a float device, or includes a water flow control valve which permits water to flow into the chamber but substantially impedes water flow from the chamber back into the gas flow passage.
Preferably, the float device controls a drain valve which controls the flow of liquid out of the water separator. In a preferred embodiment, the opening is at the lowermost part of the gas flow passage, and is relatively small compared to the cross-section of the passage and that of the water separator chamber (reservoir). In this way, water readily drains through into the water separator and reduces the amount of water that is exposed to the gas flow and is subject to possible re-entrainment. The water in the water separator is preferably transferred for use elsewhere in the fuel cell operating system for, for example, humidifying the incoming gas.
In another embodiment, the water separator chamber is substantially square or rectangular in plan view having a planar top wall which, in the installed condition on a vehicle is substantially horizontal. Four openings are located adjacent the four corners of the top wall, which forms the lower wall of the lowermost part of the gas flow passage. Preferably, each of the four openings includes a flow control valve incorporating a baffle to restrict the flow of water in a direction from the chamber to the gas passage.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.